1. Field of the Disclosure
The present application relates to an organic light emitting diode (OLED) display device and a fabricating method thereof. More particularly, the present application relates to an OLED display device adapted to enhance transmittance and yield, and to a method of fabricating the same.
2. Description of the Related Art
Recently, a variety of flat panel display devices with reduced weight and volume corresponding to disadvantages of cathode ray tube (CRT) are being developed. The flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panels (PDPs), electroluminescence (EL) devices and so on.
The electroluminescence devices are classified into an inorganic light emitting diode display device and an organic light emitting diode (OLED) display device on the basis of the formation material of an emission layer. Such electroluminescence devices have advantageous features such as high response time, high light emission efficiency, high brightness and wide viewing angle because of using self-illuminating elements.
An active matrix type OLED (AMOLED) display device controls a current flowing through an organic light emitting element using a thin film transistor, in order to display an image. Such an OLED display device can display an image in one of a top emission mode and a bottom emission mode which are based on structures of the organic light emitting element including a first electrode, a second electrode and an organic emission layer.
The bottom emission mode allows visible light emitted from the organic emission layer to be output in a downward direction of a substrate provided with the thin film transistor. On the contrary, the top emission mode forces visible light emitted from an organic emission layer to be output in an upward direction of a substrate provided with the thin film transistor. Such a bottom emission mode OLED display device can secure stability and a large process margin. However, the bottom emission mode OLED display device must be limited in aperture ratio. Due to this, the bottom emission mode OLED display device cannot be applied to high definition appliances. In view of this point, the top emission mode OLED display device with a high aperture ratio and high definition is being actively researched.
The top emission mode OLED display device can be used as a transparent display device which allows objects and/or images at its rear side opposite to a user. In detail, objects and/or images at the rear of the OLED display device are viewed by the user through the OLED display device in a switch-off state. In a switch-on state, images realized by the OLED display device can be viewed by the user.
In a transparent OLED display device of the top emission mode according to the related art, the second electrode has low transmittance. For example, transmittance of the second electrode is in a range of about 40%-50%. This transmittance value is measured from a small-sized mobile display device.
A large-sized display device increases wirings as its area is enlarged. Due to this, the large-sized display device should have a higher resistance compared to the small-sized display device. In order to lower the resistance of the large-sized display device, the second electrode can be formed thicker. In this case, transmittance of the second electrode should be lowered. As such, emission efficiency of the large-sized display device should also deteriorate.
Also, a second electrode including magnesium (Mg) is used in the top emission mode OLED display device. Such a second electrode including magnesium (Mg) can cause a short circuit in an organic light emitting element due to foreign materials. In this case, a repair process, which makes a non-emission pixel to properly emit light, should be performed for the defected organic light emitting element. However, it is difficult to apply the repair process to the top emission mode OLED display device, because magnesium (Mg) is rapidly oxidized.